7 Symptoms Of A Bad Idle Air Control Valve & Replacement Cost

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symptoms of a bad idle air control valve

As you get into your vehicle and start it, your engine suddenly sputters and behaves weirdly, and it seems as if you won’t even make it out of your garage. Yet, once you hit the road, everything seems alright and normal. However, your check engine light remains illuminated though. Therefore, what’s happening? Perhaps this is a sign of a faulty IAC valve?

If your idle develops a restless niggle, this is one of the ways your automobile communicates to you that there’s an issue that has to be resolved. Idle troubles often occur, yet not generally, due to a faulty or faulty idle control valve.

This tiny component is located in your throttle body next to your intake manifold, which works as its name implies. Luckily for workshop greasers, it’s a straightforward item to reach, maintain, and replace.

To assist others who aren’t backyard mechanics, we’ve put up a brief yet comprehensive guide regarding your idle control valves and other vital details associated with them. Read on to Learn more!.

Faulty Idle Air Control Valve Symptoms

  • Unstable Idle Speed
  • Constant Engine Stalling
  • Engine Backfire
  • Rough Idle
  • Stalling or Hesitation Under Load
  • Check Engine Light
  • Engine Won’t Start

What Is a Car’s Idle?

The idle speed of your car’s engine is the frequency at which it works while your automobile is not being driven or not having throttle inputs. Your dashboard’s speedometer gauge displays your vehicle’s idle speed in RPM or revolutions per minute. 

In other words, whenever you leave your vehicle in park mode and start your engine, that’s when your car idles.

What Is a Normal Engine Idle Speed?

The average passenger automobile idles between 500 and 1000 revolutions per minute or RPM, based on the type of automobile. Additionally, it could begin at a greater RPM, between 100 and 300 RPM, before settling down to its typical working speed.

You can check your owner’s handbook to determine the standards of your engine’s idle speed of your vehicle. High-performance automobiles might have a greater idle speed, whereas motorbikes have an idle speed of around 2,500 to 4,000 RPM.

What Is The Idle Air Control (IAC) Valve?

Your IAC valve performs exactly what its name says. They regulate the quantity of air supplied to your engine when it’s idling. Although you might believe that since your car’s engine constantly idles at approximately the same speed or RPM, its impulses are constant, this couldn’t be farther from reality.

Varying temps, oxygen ratios, and air pressure all affect the efficiency with which your engine can operate. Additionally, fluctuating engine loads significantly alter how tough your engine must work to maintain a constant RPM. When any of these parameters changes, your engine must adjust to maintain a continuous idle.

Your IAC valve is a critical feature that assists your engine in accomplishing this. It alters your intake to match the output of your engine and ensures that everything runs efficiently whenever you idle. 

What Does The Idle Air Control Valve Do?

The term “engine speed” represents the number of RPM or revolutions per minute your engine makes. This is typically known as the RPM or revolutions per minute. Your car’s current operation settings will force your idle air control valve to boost or reduce your engine’s RPM.

For example, when your car is under a significant load or is overheating, your IAC valve could change your RPM by boosting or reducing it. This enables your engine to cope with the increased load or strain in either situation.

Your ECU or engine control unit manages your IAC valve’s operation. Once this computer system gets data regarding your engine’s temp and load, it utilizes that data to regulate your IAC valve appropriately. Thus, your idle control valve would correctly control your engine RPM depending on the data conveyed by the computer.

Faulty Idle Air Control Valve Symptoms

As with any mechanical element, your idle air control valve is also subject to failure on any day or occasion. When it fails to function correctly after many years of operation, this isn’t indicative of low quality. Nonetheless, it’s relatively frequent in automotive systems.

What gets things more complicated is that, although whenever your car exhibits abnormal performance, you might not instantly identify a problem with such a little-known component.

It would be best to do a handful of actions to ascertain which component is causing the problem. Following are the details of the symptoms of a bad idle air control valve that often occur when your IAC valve fails.

Unstable Idle Speed

Unstable idle speed is among the most prevalent indications of a bad idle control valve. Your IAC valve is set to manage and sustain a steady rate of your engine idle speed.

Once your IAC valve breaks or develops a fault, your idle speed might be tossed off. This might produce an abnormally low or high idle or irregular idle speed or, in certain rare situations, a rapidly fluctuating idle speed that rises and drops frequently.

Constant Engine Stalling

When your engine stalls due to a faulty idle air control valve, you’ll be unable to operate your car at all. The moment your automobile is started, your idle air control valve would instantly fail.

If you’re out somewhere away from home and this trouble arises, the stalling would occur every few minutes at first. You must be able to reach the closest technician before your engine entirely shuts down.

Engine Backfire

When you notice flames shooting out of your tailpipe, this is referred to as a backfire. Once combustion occurs outside your engine’s combustion chambers, it backfires.  When your car backfires, this might be another sign. It’s also necessary to understand that this might suggest entirely another kind of problem.

Accelerate your car to ascertain whether the backfires result from a failing IAC valve. Allow your vehicle to decelerate and monitor any twitching. After that, inspect your exhaust pipe for leaks.  As your car decelerates, assume it twitches and petrol spills from your tailpipe. It’s most likely an IAC valve issue.

Rough Idle

A regular, efficient IAC valve can ensure that your automobile can provide smooth idling. However, when this valve fails for any cause, your car would exhibit a rough engine idle.

Rough idling could result in obnoxious vibrations whenever your car is stationary with your engine operating. Since your engine receives less air while idling, your engine will respond by vibrating dramatically.

Stalling or Hesitation Under Load

At times, your engine would stall itself, while boosting your engine’s load would lead your car to stall at other points in time. For instance, if you switch on your air-conditioner or heater while your engine suffers from a bad IAC valve, your engine would almost certainly stop quickly.

To partially resolve this issue until you get to the repair shop, just switch off your car’s heater or air conditioner and other accessories, and allow your engine to rest for a few minutes.

Check Engine Light

If there’s even the slightest issue with something linked to your engine, its central computer system will illuminate the check engine light on your dashboard. A defective idle air control valve might undoubtedly be one of the causes of this.

Once your engine control module detects an abnormal amount of revolutions per minute or RPM, it’ll alert you by activating its check engine light. Of course, there are a variety of other possible causes for this warning light to activate. You must immediately bring your car to a repair shop to have it inspected in either scenario.

Engine Won’t Start

Although unusual and unlike the most common symptoms, a defective idle air control valve might skew the air/fuel ratio enough to hinder your engine from starting, rare yet the most serious symptom.

How To Test Your Idle Air Control Valve

Occasionally, the indications of a failed air control valve are apparent. Yet, based on various other conditions, you might be unaware that the component requires care. As a result, you might conduct a fast test to assess your IAC valve’s condition.

Switch off your stereo and air conditioning and listen to the sounds your automobile creates. Following that, observe your RPMs. For passenger automobiles, the RPMs must not be less than 600 or more than 1,000rpm.

When your RPMs are excessively low, this might signify a problem with your IAC valve or any vacuum leak within your car. If your RPMs are excessive, it’s a sign that your IAC valve might need cleaning or replacement.

How To Clean A Bad Idle Air Control Valve

Although you could be inclined to replace your idle air control valve instantly, the fact is that your trouble with your IAC valve is often resolved with a simple cleaning.

Your idle control valve is relatively straightforward to access, and if you can repair it, the additional effort spent cleaning it is undoubtedly worth it.

For cleaning your idle control valve, utilize a quality degreaser and a stiff brush to scrape the edges. While you won’t be able to restore your valve to a brand new condition, you will mostly be capable of cleaning it sufficiently to restore proper operation. Follow the step-by-step guide below:

  • Remove the ducting from your air intake to your throttle body, make sure your throttle position sensor is secured.
  • Start your engine and gradually raise and maintain its idle speed between 1,000rpm to 1,500rpm.
  • Engine cleaner or throttle cleaner should be sprayed down the opening of your throttle body, aimed towards your idle control valve.
  • Let the cleaner seep through your idle air valve channel by turning off your engine and allow a few minutes to pass.
  • Start your engine and maintain an RPM range of 1,000rpm to 1,500rpm. Restart the cleaning procedure.
  • Switch off your engine again and reconnect your air intake ducting to its throttle body.
  • Restart your engine and maintain an RPM range of 1,500rpm and 2,000 rpm, or till zero white smoke emerges from your tailpipe.
  • When your idle speed continues to spike despite this procedure, your idle air control valve is faulty and must be replaced.

How to Replace a Bad Idle Air Control Valve

If you want to save some money and are mechanically savvy, you can change your bad idle control valve by yourself. It’s a straightforward fix, and we’ll guide you over anything you have to understand to get this job done!

Determine the Location of Your IAC valve.

It’s more accessible than you would believe. Idle air control valves are often located close to or on the throttle body next to your intake manifold. After finding your idle control valve, go to the following step.

Disconnect your Battery

When dealing with electrical systems, it’s necessary to detach your battery. Refusal to do so might result in static electricity that damages more components and costs you tons of dollars.

Acquire Access to your Engine’s IAC Valve

Based on your vehicle, you could be able to bypass this procedure entirely. If, however, you’re unable to access your idle control valve, you must uninstall any components impeding accessibility.

Unplug your Sensor

On the underside of your idle air control valve, there’s an electrical link that you must disconnect. Usually, these connections can be removed by hand; however, they could get blocked and challenging to release. When this occurs, a modest flathead screwdriver could often be used to remove the connection -ensure not to damage anything!

Unscrew the Bolt

Typically, your IAC valve is secured with two bolts. Unscrew both bolts and your old IAC valve cautiously.

Replace or Clean your IAC valve.

While installing the replacement idle air control valve, align the bolt slots. Bolts should be reinstalled, and the electrical connection should be reconnected.

Restore All Components That Have Been Taken

If some components were uninstalled to access your IAC valve, replace them immediately.

Reconnect your Battery

You’ve just reset your check engine light since you unplugged your battery throughout the replacement of the component. When your battery is reconnected, you’re already good to go!

IAC Valve Replacement Cost

Once the result on the voltmeter is beyond the typical band, you’ll have to acquire a brand new IAC valve. The IAC valve repair costs on average around $120 to $500, while the components price ranges between $45 to over $400, but service is only about $70.

Of course, labor costs are directly related to the technician’s hourly rate. This task would take little beyond an hour to complete, so don’t estimate a high price. Certain cars are more challenging to deal with than other vehicles, which also plays a role in pricing and effort.


Bad idle air control valve symptoms are prevalent and must not be disregarded. Otherwise, you and your automobile might suffer.

Therefore, if you ever encounter the indications detailed in this article, be sure to use the IAC valve testing techniques advised above. But, always refer to your owner’s handbook for instructions on properly handling your IAC valve.

If you’re unsure about repairing the issue yourself, seek a skilled car mechanic. The expense of resolving the problem will be minimal. It’s simpler and less expensive to fix the issues before they escalate and exhibit a more serious symptom.


Is It Safe to Drive With a Defective Idle Air Control Valve?

Are you capable? Yes. Should you do so? No. If your car has a problem, it’s always a wise approach to repair it before running it.

Can My Idle Air Control Valve Be Adjusted?

Adjusting and calibrating the throttle is usually accomplished using a machine equipped with numeric readings, a piece of equipment often held by specialists.

How Do I Remove and Clean My IAC Valve?

In most circumstances, removing your valve is not somewhat challenging. It’s always suggested to uninstall it and properly clean it before assuming it’s completely damaged.

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